1. Field of the Invention
The present invention relates to a homogenizer used, for example, to mechanically mix and agitate a plurality of liquids having no mutual compatibility to obtain an emulsion. In particular, the present invention relates to an improvement of a so-called rotor/stator type homogenizer in which a rotor is rotated at high speed inside a stator having a plurality of radially formed flow passages to thereby effect mixing and agitating by utilizing a shearing force generated between the stator and the rotor.
2. Description of the Related Art
Homogenizers are used to mechanically mix and agitate a plurality of liquids having no mutual compatibility as in the case of water and oil to thereby homogenize them into an emulsion. They are frequently used in production equipment for foods, chemical products, or the like, experimental plants, etc. Conventionally, there are known homogenizers of various structures, including what is called a rotor/stator type homogenizer.
The rotor/stator type homogenizer comprises a cylindrical stator fixed in position inside an agitation chamber and a rotor which is accommodated in a hollow of the stator and to which a predetermined r.p.m is imparted by a motor, the stator and rotor having a plurality of radially formed flow passages. Two liquids having no mutual compatibility are supplied to the hollow of the rotor by a pump provided separately from the homogenizer. When the rotor starts to rotate in the state where these liquids are being supplied, a centrifugal force is applied to the liquids, which are ejected from the radial flow passages formed in the rotor to enter the gap between the rotor and stator, entering radial flow passages of the stator. The stator does not rotate but remains stationary, so that when the rotor starts to rotate, a vortex flow is generated in the liquids existing in the radial flow passages of the rotor and the stator. Further, a shearing force in conformity with the r.p.m of the rotor is applied to the liquids having entered the gap between the rotor and the stator. Due to the energy of the vortex flow and the shearing force, the two liquids are homogenized and eventually discharged as an emulsion to the exterior through the radial flow passages formed in the stator.
To more efficiently homogenize the two liquids in this rotor/stator type homogenizer, it is important to apply a great shearing force to the liquids introduced into the gap between the rotor and the stator. For this purpose, it is important to set the gap defined between the inner peripheral surface of the stator and the outer peripheral surface of the rotor to be small, and to increase the rotor r.p.m.
However, in the conventional rotor/stator type homogenizer, the rotor rotation is supported by a ball bearing or a sliding bearing, so that when the rotor rotation accuracy, etc. are taken into account, it is impossible to set the gap between the stator and the rotor to be very small, the lower limit size of the gap being approximately 40 μm. Further, when the rotor rotates at high speed, there is the problem of wear of the bearing. To prevent particles generated as a result of the wear from mixing into the target emulsion, it is necessary to avoid operation at excessively high speed. The upper limit in operation speed is thus approximately 30000 rpm.